1. Field of the Invention
The present invention relates to a seating sensor for sensing that an occupant is seated on a vehicle seat, and more particularly, to a seating sensor including sensor cells that conduct due to a load applied by an occupant or occupants.
2. Description of the Related Art
A conventional seating sensor described in JP-A-10-39045 is disposed in a bearing surface part of a vehicle seat and includes multiple sensor cells that are connected in parallel with one another. In the seating sensor, when one sensor cell out of the multiple sensor cells conducts, a decision is made that an occupant is seated.
In view of the limitations of simple sensors, it is desirable to sense whether an occupant who is seated on a vehicle seat is an adult or a child, raising challenges. For example, compared with a range in a bearing surface part to which a load is applied when an adult is seated, a range in the bearing surface part to which a load is applied when a child is seated is narrow. In particular, the buttocks is the typical physical region of an occupant that applies a large load when the occupant is seated. A range in the bearing surface part to which the load is applied by the buttocks of a child when the child is seated may be located on the rear side of the bearing surface part or in the vicinity of the center of the bearing surface part. On the other hand, a range in the bearing surface part to which a load is applied by the buttocks of an adult when the adult is seated often extends from the center of the bearing surface part to the entire rear side of the bearing surface part. However, when an adult is seated on the front side of the bearing surface part, a range to which the load is applied may extend from the center of the bearing surface part to the entire front side thereof.
According to the seating sensor described in JP-A-10-39045, a seating state can be sensed including whether a seated occupant is an adult or a child, regardless any of the above described seating conditions. However, in the seating sensor of JP-A-10-39045, the number of sensor cells is numerous leading to increased cost. Moreover, due to the large number of sensors, any load can result in a detection event such that even when a piece of luggage is placed on the vehicle seat, any of the sensor cells may conduct leading to incorrect sensing of the seating of an occupant.
In order to solve the foregoing problem, a seating sensor, as described in JP-A-2005-153556, has been devised whereby the load bearing surface part of a vehicle seat is divided into two blocks on a vehicle front side and a vehicle rear side respectively. A sensor cell group is disposed in each of the blocks and includes multiple sensor cells that are separated from one another in a lateral direction of a vehicle. When the sensor cells included in the sensor cell group disposed at least on the front or rear side of the vehicle seat conduct simultaneously, seating of an occupant is decided. The sensor cells of the cell group are connected in series with each other and disposed on the vehicle front side of the bearing surface part, and two sensor cells that are connected in series with each other and disposed in the vehicle rear side of the bearing surface part. The cell group including the two sensor cells disposed on the vehicle front side of the bearing surface part and the cell group including the two sensor cells disposed on the vehicle rear side thereof are connected in parallel with each other. According to the seating sensor, unless at least the two sensor cells disposed on the front side or rear side conduct simultaneously, a decision is not made that an occupant is seated. Moreover, JP-A-2005-153556 describes an arrangement whereby it can be sensed whether the occupant that is seated is an adult or a child.
However, although the seating sensor described in JP-A-10-39045 has the merit of being able to sense seating of an occupant substantially all over the bearing surface part, numerous sensor cells are needed to cover the bearing surface part of the vehicle seat. From the viewpoint of a reduction in a cost, there is room for modification of the disposed positions of the sensor cells. Moreover, the seating sensor described in JP-A-2005-153556 has the merit that once the disposed positions of the sensor cells are modified, a cost can be reduced and incorrect detection of seating caused by an article such as a handbag can be diminished. However, in the above noted documents, no consideration is taken in a case where a piece of luggage is applied, where a load is applied to the vehicle right or left side of the bearing surface part due to, for example, an occupant leaning toward the right or left side of the bearing surface part, or where a load associated with a seated child is applied offering a more narrow range for sensing.
It should be noted that a piece of luggage such as, for example, a handbag when placed on a vehicle seat has a very small mass compared with an occupant. Consequently, as long as the luggage is placed on the bearing surface part of the vehicle seat so that the weight of the luggage is uniformly distributed over the bearing surface part, the possibility that any of the sensor cells will conduct is low. However, for example, if the luggage is placed on the bearing surface part against the backrest part, since the luggage enters a one-side borne state, a large load may be applied to a partial range on the bearing surface part. For example, a large load may be applied to the vehicle rear side part of the bearing surface part. In such a case, in the seating sensor described in JP-A-2005-153556, the two sensor cells disposed in the vehicle rear side conduct simultaneously creating the possibility that incorrect sensing may be caused by the luggage.